4.3.1 Data acquisition protocol

A major issue in this thesis was how to collect data in a way that minimises variations. As mentioned previously, in this thesis we only consider discrete signs. Thus we want the following aspects to be reasonably invariant:

• The location at which a sign is started, physically. This also allows us to calibrate our origin of the sign at a fixed location in space.

• The difference in the ``calibration'' between one sign and the next. In particular it was found that the fingers were subject to a slight hysteresis.

To solve this problem, it was decided that each sign would start at a fixed position around the body somewhere. A number of such locations were considered. These were narrowed down to the hand being placed on the shoulder and the hand being placed on an armrest to start with. It turned out to be very uncomfortable to touch the shoulder at the start of a sign; and in addition, the ultrasonic transmitters turned out to be less accurate when vertically aligned. Also, a fist was made at the start of each sign to minimise (although not completely remove) the effect of the calibration error.

To ensure calibration with each sign, gloverecord was programmed only to begin recording when the ``CENTER'' button the glove was pressed. Pressing the ``CENTER'' button on the glove not only sends a `00' as the key pressed, but also forces the PowerGlove to recognise this point as the new origin (ie the locations in space of all points after the last centre are relative to that centre). This also has the advantage of minimising the ``limit effect'' -- which results because of the 8-bit limit on X, Y and Z position.

To indicate the end of a sign, a particular button (``A'') is pressed on the PowerGlove. Although it might be possible to get the software to automatically stop recording when the PowerGlove re-entered the space near the origin, this would be dangerous, since it would be possible that erroneous data could result in the glove thinking it has returned to the origin, resulting in premature termination of recording. Similarly some signs could conceivably enter the space near the origin in the course of the sign itself.

The user was then asked if he wished to repeat the sign if he felt he did not ``do it right'', by pressing ``B''.

An example may help at this point.

Consider the sign for same. The gloss for same is shown in figure 4.3.

  
Figure 4.3: The Auslan Dictionary definition of same.

Gloverecord would then, in the course of asking for a sequence of signs, ask the user to make the sign same:

Please sign the word: <<<same>>>.
Press Center to begin.
Press 'B' on the glove to redo the last sign.
Press 'A' on the glove to end, once the sign is complete.

The user begins by pressing the ``Center'' button of the glove, with his hand in a fist and his arm on the armrest, shown in figure 4.4.

Gloverecord starts capturing the information from the glove at this point. It saves all frames between this and the end in a separate file.

  
Figure 4.4: The user starting the sign

The user then continues to perform the sign (see figures 4.5, 4.6 and 4.7):

  
Figure 4.5: Towards ...

  
Figure 4.6: Meeting fingers ...

  
Figure 4.7: Away ...

When the user has completed, he then tells Gloverecord to stop recording, by pressing ``A'' on the PowerGlove. If for any reason he/she is not satisfied, with the sign they just performed, they can repeat the sign by pressing ``B''.

  
Figure 4.8: The user indicates the sign is complete.